Daniel Pipes is director of the Middle East Forum and Taube/Diller distinguished visiting fellow at the Hoover Institution of Stanford University. His bi-weekly column appears regularly in newspapers around the globe. His website, DanielPipes.org, is one of the most accessed internet sources of specialized information on the Middle East and Islam.

Mark Steyn, political columnist and cultural critic, has written a remarkable book, America Alone: The End of the World As We Know It. He combines several virtues uncommonly found together - humor, accurate reportage and deep thinking - then applies these to what is arguably the most consequential issue of our time: the Islamist threat to the West.

Steyn offers a devastating thesis, but presents it in bits and pieces, so I shall pull it together here.

He begins with the legacy of two totalitarianisms. Traumatized by the electoral appeal of fascism, post-World War II European states were constructed in a top-down manner "so as to insulate almost entirely the political class from populist pressures." As a result, the establishment has "come to regard the electorate as children."

Second, the Soviet menace during the Cold War prompted American leaders, impatient with Europe's (and Canada's) weak responses, effectively to take over their defense. This benign and farsighted policy led to victory by 1991, but it also had the unintended and less salutary side-effect of freeing up Europe's funds to build a welfare state. This welfare state had several malign implications.

* The nanny state infantilized Europeans, making them worry about such pseudo-issues as climate change, while feminizing the males.

* It also neutered them, annexing "most of the core functions of adulthood," starting with the instinct to breed. From about 1980 birth rates plummeted, leaving an inadequate base for today's workers to receive their pensions.

* Structured on a pay-as-you-go basis, it amounted to an inter-generational Ponzi scheme, where today's workers depend on their children for their pensions.

* The demographic collapse meant that the indigenous peoples of countries like Russia, Italy and Spain are at the start of a population death spiral.

* It led to a collapse of confidence that, in turn, bred "civilizational exhaustion," leaving Europeans unprepared to fight for their ways.

TO KEEP the economic machine running meant accepting foreign workers. Rather than execute a long-term plan to prepare for the many millions of immigrants needed, Europe's elites punted, welcoming almost anyone who turned up. By virtue of geographic proximity, demographic overdrive and a crisis-prone environment, "Islam is now the principal supplier of new Europeans."

Arriving at a time of demographic, political and cultural weakness, Muslims are profoundly changing Europe. "Islam has youth and will, Europe has age and welfare." Put differently, "Pre-modern Islam beats post-modern Christianity."

Much of the Western world, Steyn flat-out predicts, "will not survive the 21st century, and much of it will effectively disappear within our lifetimes, including many, if not most, European countries." With even more drama, he adds that "it's the end of the world as we know it."

(In contrast, I believe that Europe still has time to avoid this fate.)

America Alone deals at length with what Steyn calls "the larger forces at play in the developed world that have left Europe too enfeebled to resist its remorseless transformation into Eurabia." Europe's successor population is already in place and "the only question is how bloody the transfer of real estate will be."

He interprets the Madrid and London bombings, as well as the murder of Theo van Gogh in Amsterdam, as opening shots in Europe's civil war and states that "Europe is the colony now."

THE TITLE `America Alone' refers to Steyn's expectation that the United States - with its "relatively healthy demographic profile" - will emerge as the lonely survivor of this crucible. "Europe is dying and America isn't." Therefore, "the Continent is up for grabs in a way that America isn't."

Steyn's target audience is primarily American: Watch out, he is saying, or the same will happen to you. Pared to its essentials, he counsels two things:

First, avoid the "bloated European welfare systems," declare them no less than a national security threat, shrink the state and emphasize the virtues of self-reliance and individual innovation.

Second, avoid "imperial understretch," don't "hunker down in Fortress America," but destroy the ideology of radical Islam, help reform Islam, and expand Western civilization to new places.

Only if Americans "can summon the will to shape at least part of the emerging world" will they have enough company to soldier on. Failing that, expect a "new Dark Ages... a planet on which much of the map is re-primitivized."

The writer, based in Philadelphia, is director of the Middle East Forum.